The majority of the buildings in the United States are residential or low-rise commercial buildings consisting of a wood frame or light-steel frame structure with wood or composition sheathing. The structure is designed to withstand the anticipated loading conditions such as rain, snow and wind. Forces and loads such as gravity, rain and snow act vertically and typically are generally predictable. Accordingly, structural designs to withstand these forces are readily available.
Lateral or shear and uplift loads such as is caused by wind, storms, hurricanes and tornadoes are difficult to predict in direction, magnitude and frequency. In a conventional framed building construction, the vertical loads are handled by the frame including studs, joists, rafters, and trusses. The lateral shear loads are dealt with using sheathing attached to the frame. In areas that have a higher risk of severe weather, such as hurricanes along the East and Gulf coasts, two layers of sheathing may be required to withstand the increased potential loads along with rafter clips and cables to prevent the roof from detaching from the framed walls.